Bill Measday <b...@measday.com> writes:
> Substantial different index use between 9.5 and 9.6

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Maybe you missed an ANALYZE after migrating? The plan difference
seems to be due to a vast difference in rowcount estimate for the
m_elevations condition:
> -> Bitmap Heap Scan on m_elevations e
> (cost=282802.21..37401439.43 rows=3512160 width=8)
> -> Seq Scan on m_elevations e
> (cost=10000000000.00..13296950520.12 rows=3512159563 width=8)
If you don't know where that factor-of-1000 came from, maybe take
it up with the postgis folk. It'd mostly be coming out of their
selectivity estimation routines.
regards, tom lane
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